The background art of the present invention will be described by taking an excavator as an example.
An ordinary excavator includes a crawler type lower travelling body, an upper slewing body mounted on the lower travelling body so as to be slewable, and a working attachment attached to the upper slewing body, the working attachment including a boom. The upper slewing body includes a cab in which an operator rides and an upper frame supporting the cab, the cab including a bottom frame forming the bottom of the cab and a plurality of pillars joined to the bottom frame.
As the above-mentioned upper slewing body, there is known an upper slewing body including an antivibration mount disposed between the cab and the upper frame. The antivibration mount is, as disclosed in Japanese Unexamined Patent Publication No. 2001-193103 and Japanese Unexamined Patent Publication No. 2009-133119, made of an elastic material such as vibration isolation rubber, and elastically deformed to permit the cab to make a relative displacement with respect to the upper frame vertically and horizontally to thereby suppress transmission of a vibration from the upper frame to the cab.
However, when the relative displacement of the cab with respect to the upper frame exceeds a permissible deformation amount of the antivibration mount due to turning over of the construction machine or the like, the elastic material constituting the antivibration mount is liable to reach its elastic limit and break. Therefore, it is desired to restrain the cab from a relative displacement with respect to the upper frame to protect the antivibration mount.
Japanese Unexamined Patent Publication No. 2001-193103 discloses a means to restrain a displacement of the cab, the means including a bolt passing through the upper frame and the cab, and a nut attached to an upper end of the bolt, the nut being operable to come into contact with an upper surface of a bottom frame of the cab to thereby restrain the displacement of the cab.
Japanese Unexamined Patent Publication No. 2009-133119 discloses a construction machine including a plate with a hole disposed on an upper frame and projecting upward, and a shaft horizontally projecting from a cab to pass through the hole of the plate with a clearance corresponding to a permissible deformation amount of an antivibration mount. The shaft comes into contact with the plate when an upward displacement, i.e., rising, of the cab with respect to the upper frame reaches the permissible deformation amount, thereby preventing the cab from excessive rising.
Either of respective technologies disclosed in Japanese Unexamined Patent Publication Nos. 2001-193103 and 2009-133119 however, is ineffective against a lateral load acting on an outer pillar of the cab, i.e., a load acting on the upper slewing body in a left-right direction or in a forward-backward direction. There can be a large lateral load acting on a joint between the bottom frame of the cab and a lower end of an outer pillar upon overturning of the construction machine or the like. The lateral load may break the joint to thereby cause the outer pillar to fall down, thus making the cab be likely to be deformed.